Rack System And Method Of Determining A Climate Condition Thereof

ABSTRACT

A rack system ( 100 ) comprises a plurality of racks ( 105 ) arranged to form at least one aisle ( 120 ) between them. The aisle ( 120 ) is sealed such that essentially all of a cooling medium supplied to the aisle ( 120 ) passes through the racks ( 105 ). A sensor arrangement ( 195 ) is provided to compare the medium pressure inside and outside the aisle ( 120 ). In one embodiment, a signal generated by the sensor arrangement ( 195 ) is used to control at least one parameter of the cooling medium supplied to the aisle ( 120 ). As an example, the flow rate of the cooling medium may be controlled.

TECHNICAL FIELD

This invention relates to a rack system to which a cooling medium suchas cooled air is supplied. The invention further relates to a method fordetermining a climate condition of the rack system. The climatecondition of the rack system may, for example, be determined in contextwith controlling one or more climate parameters within the rack system.

BACKGROUND

Electrically powered equipment, including electronic devices such ascomputers, mass storage devices and switches, are often aggregated inso-called data centres. In the data centres, it has become common tostore such equipment in racks. To allow for an easy servicing of theracks, the racks are often arranged in rows. Between two adjacent rows,an aisle is thus defined permitting servicing personal access to theequipment for installation, maintenance and removal purposes.

Most of the equipment housed inside the racks consumes enough electricalpower to heat up the ambience. As there is often a thermal limit atwhich the equipment can be operated, steps for keeping the operationaltemperature underneath a critical level have to be taken. For example,many electrical devices such as computers are equipped with fans orother internal cooling mechanisms. These mechanisms generate a flow of acooling medium such as ambient air through the devices for cooling theinternal electronic components.

However, and in particular when the electrical devices are packedtightly in the racks, the cooling effect of ambient air is often notsufficient. Moreover, ambient air tends to heat up in data centres, andthis fact additionally decreases the cooling efficiency. One approach tocombat the heating up of ambient air is the installation of climatecontrol systems in data centres. The climate control systems areconfigured to control ambient parameters such as the temperature and thehumidity of the air inside the data centres.

It has been observed that in many data centres the flow around and intothe racks of cooled and/or de-humidified air generated by the climatecontrol systems is more or less arbitrary. This results in a poorcooling efficiency. In other words, the climate control systems consumemore electrical power than actually necessary.

In order to increase the cooling efficiency, various techniques forconcentrating and directing a flow of a cooling medium towards the rackshave been proposed. In this regard, U.S. Pat. No. 6,672,955 B2 teachesan air flow management system wherein the aisles defined by two adjacentrows of racks are covered at a top end. This covering approach preventscooling medium supplied through a floor of the aisle from exiting theaisle in an upward direction. It is further suggested controlling thevolume of cooling medium supplied to the aisle via openings in thefloor, whereby the static pressure in the aisle can be controlled also.As another example, WO 2006/124240 A2 proposes baffles and doors toprevent an ambient medium from laterally entering the aisle. Thus, amixing of the ambient medium with the cooling medium (which is againsupplied through a floor of the aisle) can be prevented, and the coolingefficiency is thus increased. As a still further example, US2005/0099770 A1 teaches to fully enclose the aisle and to supply thecooling medium from the outside through the racks. According to thisapproach, the heated-up cooling medium is then collected in the enclosedaisle and can be easily removed without mixing with the cooling medium.

SUMMARY

There is a need for an improved rack system and for a technique ofdetermining a prevailing climate condition inside an aisle defined by aplurality of racks constituting the rack system. Further, there is aneed for efficiently controlling parameters of the cooling mediumdependent on the determined climate condition.

According to one aspect, a rack system is provided comprising aplurality of racks arranged to form at least one aisle between them,wherein the aisle is sealed such that essentially all of a coolingmedium supplied to the aisle passes through the racks; and a sensorarrangement allowing to compare the medium pressure inside and outsidethe aisle. The result of the pressure comparison (e.g., a pressuredifference) may be regarded as being indicative or representative of aclimate condition of the rack system.

The cooling medium may be a gaseous medium. For example, air or nitrogenmay be used in this regard. However, other cooling media known in theart may be used as well.

According to a first variant, the racks conform to an applicableindustry standard. An exemplary industry standard specifies a rack widthof 19 inch and a rack height of a certain number of predefined heightunits, with one height unit equalling 1.75 inches. In other variants,the racks may have customized dimensions. The plurality of racks in therack system may each have the same height, width and depth. Each of theracks may have a supply side for supplying the cooling medium to therack and a removal side opposite the supply side for removing thecooling medium from the rack. In one variation, the supply sides of theracks are arranged to face the interior of the aisle. The racks formingthe aisle may be housed in one or more cabinets.

The sensor arrangement may comprise a first pressure sensor locatedinside the aisle and a second pressure sensor located outside the aisle.In certain situations, the sensor arrangement may comprise multiplefirst sensors arranged in different locations inside the aisle and/ormultiple second sensors arranged in different locations outside theaisle.

The outside of the aisle as understood herein may be in fluidcommunication with the inside of the aisle. In one variation, this fluidcommunication may be part of a flow path of the cooling medium. The flowpath may be closed to form a circulation path, and the first sensor andthe second sensor may be located along the circulation path.

At least a part of the sensor arrangement (such as the first sensorand/or the second sensor) may be located at a top end of the aisle. Thesensor arrangement or a part thereof may, for example, be arranged abovethe racks or above any electrically powered equipment situated in theracks.

The system may comprise a control mechanism (such as a control unit)adapted to control at least one parameter of the cooling medium suppliedto the aisle dependent on a signal generated by the sensor arrangement.The at least one parameter of the cooling medium controlled by thecontrol mechanism may be selected from the set comprising a temperature,a humidity and a flow rate of the cooling medium. In some cases, it maybe useful to control at least two or all three of these parameters.Moreover, one or more of these parameters could also be controlledindependently from a signal generated by the sensor arrangement (e.g.,responsive to a signal generated by a further sensor not belonging tothe sensor arrangement). As there exists a physical relationship betweentemperature and humidity of the cooling medium, controlling oneparameter (such as the temperature) may at the same time result in anaccompanying control of the second parameter (such as the humidity).

The control mechanism may be responsive to a result of the pressurecomparison (e.g., to a pressure difference between the inside and theoutside of the aisle as determined by the sensor arrangement). In oneexample the control mechanism is adapted to at least maintain apredefined positive pressure inside the aisle with respect to theoutside of the aisle. For example, the control mechanism may operate ona predefined pressure set point for the positive pressure, or thecontrol mechanism ensure that a positive pressure limit is notundershot. The pressure set point or pressure limit for the positivepressure may be selected to lie approximately between 1 and 20 Pa (e.g.,between 2 and 10 Pa or at approximately 5 Pa).

In the following, various realizations and components of the controlmechanism for controlling one or more parameters of the cooling mediumwill be described in more detail. For example, at least one conveyor maybe provided for conveying the cooling medium into the aisle. The atleast conveyor may be located in a flow direction of the cooling mediumupstream or downstream of the aisle. In an upstream scenario theconveyor will thus push the cooling medium into the aisle, and in adownstream scenario the conveyor will suck the cooling medium out of theaisle.

The conveyor may be adapted to influence (e.g., to control) a flow rateof the cooling medium supplied to the aisle dependent on a signalgenerated by the sensor arrangement. The conveyor may further be adaptedto influence the flow rate dependent on signals of one or more furthersensors other than the pressure sensors of the sensor arrangement (e.g.,temperature, humidity or flow rate sensors). The conveyor may, forexample, comprise a fan having an adjustable speed. The speed may becontrolled by the control mechanism dependent on a signal generated bythe sensor arrangement.

The system may additionally comprise at least one climate control unitfor influenceing (e.g., for controlling) at least one of a temperatureand a humidity of the cooling medium supplied to the aisle. According toa first variant, the conveyor is co-located with the climate controlunit (e.g. in a single housing). According to a second variant, theconveyor is located remotely from the climate control unit.

The at least one climate control unit may be adapted to control at leastone of the temperature and the humidity of the cooling medium dependenton a signal generated by the dependent on a signal generated by thesensor arrangement. Additionally, or in the alternative, such a changeor control my be based on signals generated by one or more furthersensors other than the pressure sensors of the sensor arrangement (e.g.,temperature, humidity or flow rate sensors).

As mentioned above, at least one further sensor may be provided inaddition to the sensor arrangement configured to compare the mediumpressure inside and outside the aisle. Accordingly, at least one of thecontrol mechanism, the conveyor and the climate control unit mayadditionally, or alternatively, be controlled dependent on a signalgenerated by the further sensor. The further sensor may be located at adistance from the sensor arrangement. In one variation, the furthersensor is located far away from the plurality of racks. For example, thefurther sensor may be located in the vicinity of the climate controlunit and/or the conveyor. In such a situation, the further sensor may beconfigured to determine medium parameters before the medium enters theclimate control unit and/or the conveyor.

In one implementation, the sensor arrangement comprises a plurality offirst sensors and/or a plurality of second sensors as well as a mastercontrol unit connected to at least one of the plurality of first sensorsand the plurality of second sensors. The master control unit isconfigured to control at least one of the conveyor (e.g., responsive tothe signals of the plurality of first and second sensors) and theclimate control unit (e.g., responsive to the signals of the pluralityof first and second sensors).

In the case a plurality of first and second sensors is provided, severalfirst and second sensors may be associated with each aisle. Moreover, inthe case where the plurality of racks is arranged to form severalaisles, at least one first and second sensor may be associated with eachaisle. The control operation of the master unit may in suchconfigurations be responsive to a signal provided by the pair of firstsensor and second sensor sensing the least favourable climate condition(e.g., pressure difference).

The at least one climate control unit and the at least on conveyor mayeach comprise a slave control unit connected to the master control unit.The slave control unit may be adapted to communicate with the mastercontrol unit and to accept control commands from the master controlunit. In one realization, the slave control units are configured tocontrol at least one of the cooling medium temperature (via the at leastone climate control unit) and the flow rate of the cooling medium (viathe at least one conveyor).

The aisle may further comprise at least one bleeding opening forenabling bleeding of the cooling medium out of the aisle (and,optionally, for entering or ambient medium into the aisle). The sensorarrangement may be located close to the bleeding opening or spaced apartfrom it (e.g., spaced apart along the circulation path of the coolingmedium). Generally, the bleeding opening may be arranged in arbitrarypositions with respect to the aisle. For example, the bleeding openingmay be located at a top end, at a bottom end or somewhere between thetop end and the bottom end of the aisle. The bleeding opening may belocated essentially opposite to the location at which the cooling mediumis supplied to the aisle. If, for example, the cooling medium issupplied from the bottom of the aisle, the bleeding opening may belocated at the top end of the aisle, and vice versa.

In certain situations, the bleeding opening may be sized to preventheated-up cooling medium from collecting at a top end of the aisle(i.e., to allow the heated-up cooling medium leave the aisle via thebleeding opening). Further, at least one of the climate control unit andthe at least one conveyor may be controlled dependent on a medium flowdirection through the bleeding opening. This control is based on theconsideration that in certain situations (and depending on the size andlocation of the bleeding medium), the medium flow direction through thebleeding opening may be regarded as being indicative or representativeof a climate condition of the rack system.

The system may further comprise a cover element sealing the aisle at atop end thereof. The cover element may be transparent so that light froman outside illumination may enter the aisle. Moreover, the cover elementmay include or be spaced apart from the racks by distance elements thatare not permeable for the medium. In one implementation, the at leastone bleeding opening is accommodated in at least one of the coverelement and the distance elements.

The system may further comprise one or more terminating elements sealingthe aisle at one or more lateral ends thereof. One or more of thelateral ends may also be closed by racks. The termination elements maycomprise doors permitting servicing personal to enter and leave theaisle. The doors may be of transparent or opaque material and configuredas sliding or swing doors. In one variant, the doors are swing doorsthat can be opened up to 180° to form part of an escape route forservicing personal.

In a still further implementation, the system comprises one or moregrills for supplying the cooling medium to the aisle. The grills may,for example, be located at a top end if the cooling medium is suppliedfrom above (e.g., within a cover element of the aisle) or at a floor ofthe aisle if the cooling medium is supplied from below. In order toincrease the permeability of each grill for the cooling medium, at least70%, and preferably more than 80% (e.g., 90% or more), of the surfacearea of the grill are permeable for the cooling medium. In one variant,the grill is located at a floor of the aisle and configured such thatthe servicing personal can walk on the grill.

The system may also comprise a duct configured to supply the coolingmedium into the aisle. The duct may be situated essentially above orbelow the plurality of racks. The duct may be defined by a lower and anupper plane, wherein the upper plane defines a floor on which the racksare placed. The distance between the lower plane and the upper plane maylie for example between 150 mm and 1200 mm.

A portion of the space between the lower plane and the upper plane ofthe duct may be occupied by provisioning lines including power lines,communication lines (e.g. wire-based or fibre-optic lines) as well assupply and removal lines for fluid media such as liquids or gases. Inthe vicinity of the racks, the provisioning lines may extend through theupper plane and into the racks and/or the aisle. The locations where theprovisioning lines pierce the upper plane may be sealed using, forexample, brush strips or similar means.

The duct may be part of the medium circulation path. For example, theduct may essentially stretch between the least one climate control unitand/or the at least one conveyor on the one hand and the aisle on theother hand. Depending on whether the cooling medium is supplied to theaisle from above or from the bottom, the duct may either extend (atleast partially) over the aisle or below the aisle. Moreover, the ductmay be configured such that the cooling medium is supplied to aplurality of aisles simultaneously.

Each of the racks may comprise one or more mounting spaces foraccommodating payload. Mounting spaces that are not occupied by payloadmay be sealed (e.g., by blanking panels) to prevent a significant flowof ambient medium into the aisle and/or a significant leakage of coolingmedium out of the aisle. It should be noted that no 100% sealing isgenerally required, but any leaks will typically degrade the overallcooling efficiency of the system.

The payload situated in the mounting spaces may comprise electricallypowered equipment. Such equipment may comprise computers (e.g. servers),mass storage devices, processing units, network elements such asswitches, hubs, routers, and so on. The payload and in particular theelectrically powered equipment may comprise a private medium conveyor(e.g., an internal fan) for conveying cooling medium from the supplyside to the removal side of the rack. In one arrangement, all thepayload inside a rack is arranged such that the supply sides of theprivate medium conveyors match the supply side of the rack, and theremoval sides of the private medium conveyors match the removal side ofthe rack.

Each item of payload may comprise a controller for controlling theprivate medium conveyor (e.g., on the basis of payload parameters suchas sensor readings or a determined state of the payload). Each item ofpayload may additionally comprise a communication mechanism forexchanging information about its internal state and the performance andcurrent operating point of its private medium conveyor with otherdevices. Such other devices may include the master control unit, the atleast one conveyor for conveying the cooling medium into the aisle andthe at least one climate control unit.

The system may further comprise a housing in which the aisle is located.The housing can be adapted to close the circulation path of the coolingmedium. The housing may comprise the floor, ceiling and walls of a datacentre room. In one implementation, the at least one conveyor and/or theat least one climate control unit are situated inside or close to thehousing. The climate control unit may, of course, also be situatedoutside the housing. In this case, further ducts may be provided topermit a flow of ambient medium from the housing to the climate controlunit and a back flow of the cooling medium (e.g., of the cooled-downambient medium). Similar to the climate control unit, the at least oneconveyor for conveying the cooling medium into the aisle may likewise belocated either within or outside the housing.

The climate control unit may be fed by the ambient medium (including, inthe case of a closed circulation path, the heated-up cooling mediumexiting the racks), perform climate control on the ambient medium so asto convert the ambient medium into the cooling medium, and then forwardthe cooling medium (with the help of the at least one conveyor) throughthe duct towards the aisle. In this way, the closed circulation path maybe established.

According to a further aspect, a method for determining a climatecondition of a rack system comprising a plurality of racks arranged toform an aisle between them is provided. The method comprises supplying acooling medium into the aisle, wherein the aisle is sealed such thatessentially all of the cooling medium supplied to the aisle passes tothe racks, and comparing the medium pressure inside and outside theaisle to determine the climate condition. The result of the pressurecomparison (e.g., a pressure difference) may be regarded as beingindicative or representative of a climate condition pertaining to therack system.

The method may further comprise controlling at least one parameter ofthe cooling medium supplied to the aisle dependent on the result of thecomparison. The at least one parameter may be selected from a setcomprising a temperature, a humidity and flow rate of the coolingmedium. In one variation, the flow rate is controlled such that apredefined pressure difference in the aisle is at least maintained(e.g., is not exceeded and/or not undershot).

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, further advantages and details of the presentinvention will be discussed with reference to the drawings, wherein:

FIG. 1 shows a perspective view of a rack system embodiment;

FIG. 2 shows an embodiment of a rack system control layout;

FIG. 3 shows a schematic diagram of a first method embodiment.

FIG. 4 shows a schematic diagram of a second method embodiment;

FIG. 5 shows a top view of a data centre comprising a multi-aisle racksystem;

FIGS. 6 a and 6 b show two exemplary server racks that can be used forrealizing an embodiment of a rack system;

FIG. 7 shows a photograph of an aisle including a floor grill and twoparallel rows of racks;

FIG. 8 shows a rack system layout without separation of cold and warmaisles; and

FIG. 9 shows another rack system layout without separation of cold andwarm aisles.

DETAILED DESCRIPTION

FIG. 1 shows a perspective view of an embodiment of a rack system 100.The rack system 100 is housed in a data centre room (not shown) that mayadditionally contain further rack systems.

The rack system 100 comprises a plurality of individual racks 105. Theracks 105 are arranged “front-to-front” in two parallel rows 110, 115such that an aisle 120 is formed between them. In the embodiment shownin FIG. 1, each row 110, 115 of racks 105 is additionally enclosed by arespective cabinet 125, 130.

The individual racks 105 define mounting spaces for electrically poweredequipment (not shown). In the present embodiment, the electricallypowered equipment comprises computer servers and mass storage deviceswith internal private medium conveyors (such as fans) for propelling acooling medium through a chassis thereof. The electrically poweredequipment is arranged in the racks 105 such that a medium supply side ofeach item of electrically powered equipment faces the aisle 120, and amedium removal side faces the opposite direction. The media supply sidesand the media removal sides of the electrically powered equipment thusdefine the medium supply sides and medium removal sides of theindividual racks 105.

As shown in FIG. 1, the aisle 120 is sealed in such a manner thatessentially all of a cooling medium supplied to the aisle 120 passesthrough the racks 105. In other words, the cooling medium issubstantially prevented from exiting the aisle 120 in other directionsthan through the racks 105. Rack portions not occupied by electricallypowered equipment requiring cooling may be sealed using, for example,blanking panels. It should be noted in this regard that no completesealing of the aisle 120 is required (nor technically possible withreasonable technical efforts). In other words, a certain leakage ofcooling medium will in many cases be tolerable as long as the leakagedoes not substantially degrade the cooling efficiency.

In the embodiment shown in FIG. 1, several sealing members are providedto enclose the aisle 120 in the aisle portions not limited by the rackcabinets 125, 130 housing the racks 105. Specifically, a cover element135 is sealing the aisle 120 at a top end thereof. The cover element 120is made from a transparent material such as acrylic glass and permitslight from the data centre illumination enter the aisle 120. The coverelement 135 comprises lateral distance elements 140, 145 so that theplane defined by the cover element 120 is spaced apart from the planedefined by the upper surfaces of the two cabinets 125, 130.

The sealing members enclosing the aisle 120 additionally comprise twolateral terminating elements 150, 155. The lateral terminating elements150, 155 are configured as swing doors allowing servicing personal toenter and leave the aisle 120. It should be noted that one of thelateral terminating elements 150, 155 could be replaced by a cabinethousing one or more further racks 105. Moreover, alternative doorconstructions such as sliding doors could be used as well.

Cooling medium such as air is provided to the aisle 120 via a floor ofthe aisle, i.e. from the bottom. To this end, an elevated floor system160 is provided. The elevated floor system 160 defines a duct 165between a lower plane 170 and an upper plane 175 of the elevated floorsystem 160. As shown in FIG. 1, the rack cabinets 125, 130 and the aisle120 defined between them are located on the upper plane 175.

The upper plane 175 of the elevated floor system 160 includes aplurality of openings (not shown in FIG. 1) for fluidically connectingthe aisle 120 to the duct 165. A cooling medium fed into the duct 165 asillustrated by arrows 180 can thus enter aisle 120 through its floor.Due to the sealing members enclosing the aisle 120, the cooling mediumentering the aisle 120 can leave the aisle 120 only through the racks105 as indicated by arrows 185. Specifically, the private mediumconveyors of the electrically powered equipment situated in mountingspaces of the racks 105 convey or propel the cooling medium entering theaisle 120 through the racks 105. The cooling medium thus transferredthrough the racks 105 is heated-up by the heat dissipated from theelectronically powered equipment and leaves the racks 105 as indicatedby arrows 190.

The path of the heated-up cooling medium exiting the racks 105 can beclosed by cooling down (and, optionally, dehumidifying) the heated-upcooling medium leaving the racks 105 and by feeding the cooled-down(and, optionally, dehumidified) medium again into the duct 165. Itshould be noted that in other embodiments, the medium flow path need notbe closed within the data centre. In such embodiments the heated-upcooling medium leaving the racks 105 may simply be conveyed out of thedata centre into the environment.

It is evident that the parameters of the cooling medium supplied via theduct 165 to have to be tightly controlled to make sure that heatgenerated by the electrically powered equipment can be efficientlydissipated, preventing any undesirable heat build-up within the racks105. On the other hand, it is apparent that an excessive adjustment ofthe cooling medium parameters (e.g., an excessive cooling down) shouldbe avoided to increase energy efficiency.

To efficiently control one or more parameters of the cooling mediumsupplied to the aisle 120, a sensor arrangement 195 is provided at a topend of the aisle 120. The sensor arrangement 195 comprises two or morepressure sensors for comparing the medium pressure inside and outsidethe aisle 120.

In the following, one exemplary embodiment for controlling a parameterof the cooling medium based on signals received from the sensorarrangement 195 will be discussed in context with the schematic controldiagram of FIG. 2. In the specific embodiment shown in FIG. 2, the samereference numerals as in FIG. 1 will be used to designate the same orsimilar elements.

The control embodiment as illustrated in FIG. 2 is based on a closedcirculation path of the cooling medium. The closed circulation pathcomprises at least one down flow unit 205 located within the data centreroom that also houses the aisle 120. In alternative embodiments, thedown flow unit 205 could be located outside this room provided that itremains in fluid communication therewith in a similar manner as shown inFIG. 2.

The down flow unit 205 comprises two dedicated components in a singlehousing, namely a climate control unit 210 on the one hand and a coolingmedium conveyor 215 on the other hand. The climate control unit 210 is aso-called chiller, which is attached to a cold water supply tube 220 anda warm water removal tube 225. The cold water supplied via the tube 220may have a temperature of approximately 5 to 15° C. (e.g., between 11and 13° C.). The warm water removed via tube 225 may have a temperatureof approximately 12 to 22° C. (e.g., between 16 and 19° C.).

Ambient medium passing through the climate control unit 210 is broughtinto thermal contact with the cold water and thus cooled down. At thesame time, the cold water is heated-up and removed from the climatecontrol unit 210 via the warm water removal tube 225. Optionally, theambient medium is additionally subjected to a dehumidifying step in theclimate control unit 210.

The conveyor 215 conveys the cooled-down ambient medium as coolingmedium into the duct 165. In the vicinity of where the cooling medium isfed into the duct 165, a temperature sensor 235 coupled to a controlunit 240 is provided. The temperature sensor 235 is configured to sensethe current temperature of the cooling medium. In the control unit 240,the current temperature of cooling medium is then compared with atemperature set point, and a cold water supply valve 245 located in thecold water supply tube 220 is controlled dependent on a result of thiscomparison.

The cold water supply valve 245 controls the flow of cold water throughthe climate control unit 210 such that the medium temperature sensed bythe sensor 235 approaches or equals a specific temperature set point. Asillustrated in FIG. 2, the temperature of the cooling medium enteringthe duct 165 will typically be set to a value in the range betweenapproximately 18 and 26° C. (e.g. at 20, 21, 22, 23 or 24° C.).

In the embodiment illustrated in FIG. 2, control of the cooling mediumtemperature is performed autonomously. In other words, the control unit240 operates solely on the signal generated by the temperature sensor235. In other embodiments, the control unit 240 may additionally, or inthe alternative, take into account the signals of one or more othersensors shown in FIG. 2 and discussed hereinafter.

As has been mentioned above, the ambient medium cooled down by theclimate control unit 210 is propelled by the conveyor 215 into the duct165. The conveyor 215 is configured as a fan the speed of which beingcontrollable to adjust the flow rate (medium speed) of the coolingmedium supplied into the duct 165 under control of a dedicated controlunit 250. During normal operation, the conveyer 215 may propel thecooling medium at a speed of 1 to 3 m/s (e.g., at approximately 1.5 to2.2 m/s).

In order to achieve a desired flow rate of the cooling medium, therequired medium speed depends on the height of the duct 165 along whichthe cooling medium is propelled from the down flow unit 205 to the aisle120. The medium speed values mentioned above correspond to a nominalduct height of approximately 400 to 600 mm. In cases of smaller ductheights (of, e.g., 150 mm), the speed may need to be increased, and incases of larger duct heights (of, e.g., 800 mm), the speed may need tobe reduced. Generally, the medium speed and the height of the duct 165are selected such that the medium pressure inside the duct 165 iscomparatively low, for instance no more than 20 Pa (e.g., no more than10 Pa) over the medium pressure inside the data centre outside the aisle120.

As illustrated in FIG. 2, the cooling medium propelled through the duct165 (at a speed of approximately 1.7 m/s and at an increased pressure ofless than approximately 10 Pa compared to the pressure inside the datacentre) enters the aisle 120 via openings 255 in the upper floor plane175. Inside the aisle 120, a medium temperature of typically 22 to 26°can thus be maintained, which is significantly lower than the ambienttemperature of 32 to 38°. As indicated by the arrows in FIG. 2, thecooling medium entering the aisle 120 will be conveyed or propelled bythe private medium conveyors of the electrically powered equipment tothe outside of the aisle 120 and will at the same time be heated-up whentaking up heat within the electrically powered equipment. The heated-upcooling medium leaving the racks becomes part of the ambient medium andwill flow back to the down flow unit 205 thus establishing a closedcirculation path.

Turning now to the sensor-based control of cooling medium parameters,and with continuing reference to FIG. 2, the sensor arrangement 195comprises a first pressure sensor 195A located at the top inside theaisle 120 as well as a second pressure sensor 195B located outside theaisle. The sensor arrangement 195 including the two pressure sensors195A and 195A is configured to compare the medium pressure inside andoutside the aisle 120. To this end, the first pressure sensor 195Asenses the medium pressure inside the aisle 120 and the second pressuresensor determines the medium pressure outside the aisle 120.

As becomes apparent from FIG. 2, the two pressure sensors 195A and 195Bare located at positions that are in fluid communication with each otherfrom the perspective of the flow path of the cooling medium through theracks. For this reason, the pressure difference determined as a resultof a comparison of the medium pressures detected by the two pressuresensors 195A and 195B is indicative of a medium flow (e.g., anapproximate flow direction or flow rate) through the racks. The pressuredifference thus detected can therefore be evaluated and used for controlpurposes regarding one or more parameters of the cooling medium.

The pressure sensors 195A and 195B are connected to the control unit 250associated with the conveyor 215. Via the connection, the pressuresensors 195A and 195B signal their respective pressure measurement tothe control unit 150. The control unit 250 evaluates the pressuremeasurements by comparing the medium pressure inside and outside theaisle 120 to thus determine the pressure difference. The comparisonroutine applied by the control unit 250 can be regarded as being part ofthe sensor arrangement 195, but in other embodiments the comparisoncould also be performed by a dedicated comparison unit belonging to thesensor arrangement 195 and coupled to the control unit 250.

Based on the pressure difference, which is indicative of a medium flowthrough the racks, the control unit 250 controls the speed (and thus theflow rate) of the cooling medium propelled by the conveyor 215 such thatthe appropriate volume of cooling medium is fed to the aisle 120. In afurther mode, the conveyor 215 may additionally be controlled dependenton the signal of one or more further sensors, such as an optionaltemperature sensor 260 located outside the aisle 120 and preferablyclose to an intake of the down flow unit 205.

In the following, the control of the conveyor 215 by the control unit250 responsive to the detected pressure difference will be described inmore detail with reference to the flow chart 300 of FIG. 3.

Referring to the flow chart 300 of FIG. 3, the control operation withrespect to the conveyor 215 starts with supplying the cooling mediuminto the aisle 120 (step 302). The cooling medium will thus fill theaisle 120 from the bottom until it reaches the cover element 135. As theaisle 120 is sealed both laterally and on its top (see FIG. 1),essentially all of the cooling medium entering the aisle 120 through theopening 255 will pass trough the racks 105 and can thus be utilized foran efficient heat dissipation within the electrically powered equipmentmounted in the racks 105. The flow of cooling medium through the racksmanifests itself in a certain positive pressure inside the aisle 120compared to the ambience of the aisle 120.

Should the equipment inside the racks 105 require to dissipate more heat(and therefore require more cooling), the private medium conveyors ofthe equipment will propel more cooling medium from the aisle 120 throughthe racks 105. As a result, the pressure inside the aisle 120 asdetected by the pressure sensor 195A with respect to the ambiencepressure as detected by the pressure sensor 195B will drop slightly.This drop of the pressure difference (and the resulting decrease of thepositive pressure inside the aisle 120) will be detected by thecomparison performed in step 304 by the control unit 250 (e.g., bycomparing the determined positive pressure or pressure difference with apredefined pressure set point). The drop can be interpreted as a requestfor more cooling medium 120. As a result, the control unit 250 controlsthe conveyer 215 such that the medium speed (and thus the flow rate)increases. Therefore, more cooling medium per time unit is propelledthrough the duct 165.

Once slightly more cooling medium is introduced into the aisle 120 pertime unit than is propelled by the private medium conveyors through theracks 105 out of the aisle 120, the pressure of cooling medium insidethe aisle 120 will gradually rise again. At the same time, the pressuredifference between the aisle 120 and the ambience will increase. Thecontrol unit 250 can thus determine based on the increasing pressuredifference that enough cooling medium is fed into the aisle 120 and canstart gradually decreasing the speed (and thus the flow rate) of coolingmedium through the duct 165 until the specific pressure set point isreached again.

The pressure set point applied by the control unit may lie in the rangebetween 2 and 10 Pa (e.g., at approximately 4, 5 or 6 Pa) and may bedynamically defined based on the cooling medium temperature (as measuredby the temperature sensor 235) adjusted by the control unit 240. A setpoint has the advantage that the control scenario that can beimplemented by the control unit 250 is not restricted to increasing theflow rate starting from a specific nominal flow rate, but can also startwith an initial flow rate decrease. Accordingly, should the electricallypowered equipment located in the racks have less power to dissipate (andshould their private medium conveyors therefore propel less coolingmedium from the aisle 120 through the racks 105), the pressuredifference may rise with respect to the pressure set point. This rise ofthe pressure difference can be interpreted by the control unit 250 as anexcess of cooling medium supplied to the aisle 120, and the propellingof cooling medium into the duct 165 (i.e. the medium speed) may bedecreased. Of course, control strategies not relying on a pressure setpoint could be implemented as well. Such control strategies may, forexample, be based on a minimum pressure difference limit that should notbe undershot (but may be exceeded).

Returning to FIG. 2, the function of an optional bleeding opening 197provided at a top end of the aisle 120 in the cover element 135 will nowbe briefly explained. While the bleeding opening 197 is schematicallyillustrated to be spaced apart from the pressure sensors 195A and 195B,it could also be located close to one or both pressure sensors 195A and195B. Moreover, while only one single bleeding opening 197 is shown, itis clear that multiple such bleeding openings could be provided for theaisle 120.

The optional bleeding opening 197 has a fixed or adjustable diameterwith a size ranging for example anywhere between a fully closed position(or a small size such as 10 cm²) and 500 cm² (e.g., between 80 cm² and200 cm²). The bleeding opening 197 may be provided to enable a bleedingof the cooling medium out of the aisle 120 (and an optional entering ofan ambient medium into the aisle 120). In certain operational situationsthere is a likelihood that cooling medium inside the aisle 120 will beheated up by thermal heat transfer from the warmer racks and the chassisof electrically powered equipment stored therein. The heated-up coolingmedium is collecting at the top end of the aisle 120 and would degradethe cooling efficiency if sucked in by internal fans of the electricallypowered equipment. Advantageously, the bleeding opening 197 allows theheated-up cooling medium leave the aisle 197, which improves the overallcooling efficiency. Due to the simultaneously maintained positivepressure inside the aisle 120, no ambient medium will enter the aisle120 through the bleeding opening 197 under normal operating conditions.

In an embodiment not illustrated in the drawings, an optional furthersensor may be provided in the vicinity of the bleeding opening 197 (or asecond bleeding opening spaced apart from the bleeding opening 197) andmay be configured to determine a medium flow direction through thebleeding opening. The further sensor may, for example, be a temperaturesensor. The temperature sensed by the temperature sensor will generallybe higher if cooling medium leaves the bleeding opening 197 into theambience compared to climate situations in which warmer medium entersthe aisle 120 from the ambience via the bleeding opening 197. Theentering of medium through the bleeding opening 197 into the aisle 120may, for example, be the result of a failure of the sensing arrangement195 or of unusual operating conditions.

The medium flow direction sensed by the temperature sensor is indicativeor representative of a climate condition within the aisle 120 inrelation to the cooling medium. Dependent on the medium flow directionsensed by the temperature sensor, one or more parameters of the coolingmedium (such as its flow rate) can be controlled to allow for anenergy-efficient cooling of the electrically powered equipment mountedin the racks 105. To this end, the control unit 250 may additionally beconnected to the temperature sensor and perform its control tasks alsodependent on the temperature sensed in the vicinity of the bleedingopening.

In the following, a further embodiment for controlling the conveyor 215will be described with reference to the flow chart 400 of FIG. 4. Thecontrol embodiment illustrated in FIG. 4 can be performed concurrentlyor as an alternative to the control embodiment discussed above incontext with FIG. 3.

In a first step 402, the pressure difference (as an exemplary parameter)of the cooling medium inside and outside this aisle is maintained at apredetermined value In step 404, the cooling medium is advanced by theconveyor 215 through the duct 165 into the aisle 120 and to the mediumsupply sides of the racks 105. Then, in step 406, it is determined if aturnover of cooling medium through the racks 105 differs from a turnoverof cooling medium through the conveyor 215. Such a turnover differencemay manifest itself in a change of the pressure difference between theinside and the outside of the aisle 120 and may thus be detected by thesensor arrangement 195.

In a further step 408, the conveyor 215 is controlled dependent on theturnover difference determined in step 406. This control may, forexample, target at minimizing the turnover difference or at keeping theturnover difference at a predetermined value.

It should be noted that steps 402 to 408 will in a typically scenario beperformed concurrently and repeatedly. Moreover, as has been explainedabove, the turnover difference and any changes in the turnoverdifference may be detected based on a comparison of pressure valuessensed by the pressure sensors 195A and 195B. In other words, when theturnover through the racks is higher than the turnover through theconveyor, the pressure difference will rise, and vice versa.

As a result of the control approach illustrated in FIGS. 1 to 4 inrelation to the conveyor 215, the power consumption of the conveyor 215can be reduced as the speed of its fan can be selectively decreased insituations in which the electrically powered equipment mounted in theracks 105 requires less cooling.

While the embodiments discussed above comprise only a single sensorarrangement 195 comprising a single pressure sensor 195A inside theaisle 120 and a single pressure sensor 195B outside the aisle 120, itwill be appreciated that two or more pressure sensors 195A could belocated at spaced-apart positions for example in the upper portion ofthe aisle 120. Additionally, or in the alternative, two or more pressuresensors 195B could be arranged at spaced-apart positions outside theaisle 120. In such a situation, each of the multiple pressure sensorswill be coupled to the control unit 250. The control unit 250 may thenperform its control tasks for example based on the external pressurevalue detected by any of the internal pressure sensors 195A and theexternal value detected by any of the external pressure sensors 195B.Moreover, it will be appreciated that also the number of aisles 120coupled to the duct 165 may be increased as required. In this regard,reference is made to the schematic rack system layout illustrated inFIG. 5. Again, identical reference numerals will be used to identify thesame or similar components.

According to the rack system layout shown in FIG. 5, four parallelaisles 120 are provided, each aisle 120 being defined by two parallelrows 110, 115 of racks (only two rows are specifically denoted in FIG.5). The individual aisles 120 are all coupled to the same duct (seereference numeral 165 in FIGS. 1 and 2). Each row 110, 115 of rackscomprises either 9 or 10 rack units. Each aisle 120 comprises at leastone sensor arrangement 195.

The aisles 120 are provided with cooling medium from six individual downflow units 205. A master control unit (not shown) is responsible fordown flow unit management, and the six down flow units 205 are connectedas slave units to the master control unit. The master control unitincorporates the control functions discussed above in connection withthe control unit 250 plus additional control functions for down flowunit management.

The master control unit is configured to perform its control operationsresponsive to the least favourable (e.g., smallest positive or largestnegative) pressure difference detected by any of the multiple sensorarrangements 195 distributed over the individual aisles 120. Dependingon the cooling requirements, the master control unit switches individualdown flow units on, off or into a standby mode. Additionally, the mastercontrol unit controls the fan speed of the conveyors associated withdown flow units 205 that have been switched on (in a range between 30 to100% of the maximum speed) dependent on the detected least favourablepressure difference.

While the master control unit thus centrally controls the total flowrate of the cooling medium, each down flow unit 205 may autonomously andlocally control temperature and humidity of the cooling medium passingthe individual down flow unit 205. The temperature and humidity controlof the individual down flow units may be based on a temperature setpoint received from the master control unit.

The overall control concept is identical to the control conceptdiscussed above in context with FIGS. 1 to 4. In other words, in a firststep the least favourable pressure difference detected by any of thedistributed sensor arrangements 195 is compared to a pressure set point.If the least favourable pressure difference higher than the pressure setpoint applied by the master control unit, this is an indication that thedown flow units 205 deliver too much cooling medium to the individualaisles 120. Accordingly, the flow rate of cooling medium will bedecreased. If, on the other hand, the least favourable pressuredifference is lower than the pressure set point, this can be seen as anindication that the down flow units 205 deliver not enough coolingmedium to the individual aisles 120. Accordingly, the flow rate ofcooling medium will be increased. As mentioned above, possible measuresfor controlling the flow rate include switching individual down flowunit 205 on or off, and controlling the fan speed of the down flow units205 that have been switched on. Control strategies that may be appliedby the controllers 240, 250 shown in FIG. 2 and the master control unitinclude a PI control which, as such, is known in the art.

FIG. 6 illustrates an embodiment of a rack 105 that comprises aplurality of mounting spaces for accommodating payload includingelectrically powered equipment. Specifically, FIG. 6 a shows the emptyrack 105 that may form the basis for the rack systems discussed above incontext with FIGS. 1 to 5. Unused mounting spaces of the rack 105 may becovered with blanking panels as shown in FIG. 6 b. The blanking panelsensure that cooling medium supplied to the aisle 120 does not leak outof the racks 105. It should again be noted here that no 100% sealing isrequired to permit an efficient cooling operation.

FIG. 7 shows an illustration of the floor of the aisle 120. As can beseen in FIG. 7, the floor is completely covered by a grill 705. Thegrill 705 has a large open surface area. Specifically, approximately 90%of the surface area of the grill 705 is permeable for the coolingmedium. As a result of using the grill 705 as illustrated in FIG. 7,only a comparatively small pressure difference between the duct 165 onthe one hand and the ambience of the aisle 120 on the other is requiredto efficiently supply cooling medium to the aisle 120, which againpermits operating the conveyors inside the down flow units at lowspeeds. As has been mentioned above, a pressure difference of less than10 Pa will in many cases be sufficient.

The various cooling approaches discussed herein provide significantadvantages over prior art cooling approaches as illustrated, forexample, in FIGS. 8 and 9. FIG. 8 shows a rack system layout withoutcold and hot aisle separation. This kind of rack system layout is commonin data centres that host legacy systems and that were not specificallytailored to support a ventilation path inside the data centre. As can beseen in the ellipses, there are various regions in which fresh coolingmedium supplied from the floor and heated-up cooling medium exiting theracks gets mixed. Such a mixing reduces the cooling efficiency of thedata centre significantly. FIG. 9 shows another variant of a rack systemlayout inside the data centre, this time with cold and hot aisleseparation. As shown by the ellipsis, there is still a zone where freshcooling medium and heated-up cooling medium can mix.

Comparing the operational parameters shown for the rack system layoutsin FIGS. 8 and 9 with the operational parameters shown in FIG. 2, itbecomes apparent that the cooling approach discussed herein can beincorporated using much lower medium speeds and pressure differences.Additionally, the cooling medium exiting the down flow units 205 neednot be cooled as much as in the legacy approaches, which also adds tothe overall cooling efficiency.

While the present invention has been described with respect toparticular embodiments, those skilled in the art will recognize that thepresent invention is not limited to the specific embodiments describedand illustrated herein. Therefore, it is to be understood that thisdisclosure is only illustrative. Accordingly, it is intended that theinvention be limited only by the scope of the claims appended hereto.

1. A rack system, comprising a plurality of racks arranged to form atleast one aisle between them, wherein the aisle is sealed such thatessentially aN of a cooling medium supplied to the aisle passes throughthe racks, and wherein a top end of the aisle is sealed by a coverelement; and a sensor arrangement configured to compare the mediumpressure inside and outside the aisle.
 2. The system of claim 1, whereinthe sensor arrangement comprises a first pressure sensor that is locatedinside the aisle and a second pressure sensor that is located outsidethe aisle.
 3. The system of claim 2, wherein a circulation path for thecooling medium is provided, and wherein the first sensor and the secondsensor are located along the circulation path.
 4. The system of claim 1,wherein at least a part of the sensor arrangement is located at a topend of the aisle.
 5. The system of claim 1, further comprising a controlmechanism adapted to control at least one parameter of the coolingmedium supplied to the aisle dependent on a signal generated by thesensor arrangement.
 6. The system of claim 5, wherein the at least oneparameter is selected from the set comprising a temperature, a humidityand a flow rate of the cooling medium.
 7. The system of claim 5, whereinthe control mechanism is responsive to a pressure difference between theinside and the outside of the aisle determined by the sensorarrangement.
 8. The system of claim 5, wherein the control mechanism isadapted to at least maintain a predefined positive pressure inside theaisle with respect to the outside of the aisle.
 9. The system of claim8, wherein the positive pressure is selected to lie between 1 and 20 Pa.10. The system of claim 1, further comprising at least one conveyor forconveying the cooling medium into the aisle.
 11. The system of claim 10,wherein the at least one conveyor is adapted to influencing a flow rateof the cooling medium supplied to the aisle dependent on a signalgenerated by the sensor arrangement.
 12. The system of claim 1, furthercomprising at least one climate control unit for influencing at leastone of a temperature and a humidity of the cooling medium supplied tothe aisle.
 13. The system of claim 12, wherein the at least one climatecontrol unit is adapted to influence at least one of the temperature andthe humidity of the cooling medium dependent on a signal generated bythe sensor arrangement.
 14. The system of claim 1, further at least onebleeding opening for enabling bleeding of the cooling medium out of theaisle, wherein the bleeding opening 15 preferably located at a top endof the aisle.
 15. The system of claim 14, wherein the sensor arrangementis spaced apart from the bleeding opening along a circulation path ofthe cooling medium.
 16. The system of claim 1, further comprising one ormore terminating elements sealing the aisle at one or more lateral ends.17. The system of claim 1, further comprising a grill for supplying thecooling medium to the aisle, the grill being located at a floor of theaisle.
 18. The system of claim 1, further comprising a duct configuredto supply the cooling medium into the aisle.
 19. The system of claim 18,wherein the duct is configured to supply the cooling medium to aplurality of aisles.
 20. The system of claim 18, wherein the duct issituated essentially below the plurality of racks.
 21. A method fordetermining a climate condition of a rack system comprising a pluralityof racks arranged to form an aisle between them, the method comprising:supplying a cooling medium into the aisle, wherein the aisle is sealedsuch that essentially all of the cooling medium supplied to the aislepasses through the racks, and wherein a top end of the aisle is sealedby a cover element; and comparing the medium pressure inside and outsidethe aisle to determine the climate condition.
 22. The method of claim21, further comprising controlling at least one parameter of the coolingmedium supplied to the aisle dependent on a result of the comparison.23. The method of claim 22, wherein the at least one parameter isselected from the set comprising a temperature, a humidity and a flowrate of the cooling medium.
 24. The method of claim 23, wherein the flowrate is controlled to at least maintain a predefined positive pressureinside the aisle with respect to the outside of the aisle. 25.(canceled)